1. Field of the invention
This invention relates to a latex for immunoserological tests and a method therefor.
2. Description of the prior art
Along with the progress in immunoserology, improvements in the techniques of clinical examinations are remarkable. In immunoserological examinations, test tubes are used, and for the dilution of the serum, measuring pipettes are employed. Both the complexity of the procedures of using such test tubes and pipettes, and the handling of large numbers of specimens caused by the increased numbers of examinations made, are factors in lowering the accuracy of immunoserological tests. However, with the introduction of automation into clinical examinations, as well as in the realm of immunoserology, the amount of blood taken from the patient has decreased, and the small-volume test method, or microtitration method, in which exact clinical data is obtained using small amounts of test reagents, is now being used. The microtitration method was proposed in 1955 by the Hungarian researcher Takatsy, and in 1962 the American worker Sever suggested improvements. In 1963 in the United States, a microtitration kit was made commercially available, and since then, this kit has been accepted and used for immunoserological tests all over the world. In 1967, the Center for Disease Control (CDC) in the United States adopted this kit as the standard test method for complement fixation reactions. The microtitration method is used in the training manual of the Public Health Service. This kit became known to workers in the field of virology in Japan relatively early, and the imported kits are being used in virus immunoserological examinations (hemagglutination reactions, hemagglutination inhibition reactions, complement fixation reactions, etc.) and in the culture of cells and tissues. The characteristics of the microtitration method are: (1) with only a small volume of serum, a number of different tests can be done, (2) the operating procedure is simple, and many specimens can be speedily diluted in a short time, (3) the method is economical, because compared to other existing methods, only small amounts of antigen, antiserum, reagents, and so on are used, (4) the whole reaction can be seen on one plate, and detailed evaluation of agglutination and hemolysis is easy, and (5) this method has the same sensitivity and accuracy as other existing methods, with excellent reproducibility as well. In the microtitration method, blood cells of relatively high specific gravity are used, such as those taken from the red blood cells of sheep or chickens. When these blood cells from animals are stored, the putrefaction and denaturation of the cells are rapid, and storage for long periods is not possible; also, because there are large individual differences in the cells, the scatter of the test values is wide, and accurate data are difficult to obtain. These and other problems exist with this method. In addition, blood cells themselves contain antigens, which react with the various antigens in the serum being tested, easily giving rise to ambiguous reactions as a result. As a substitute for these blood cells, synthetic latex has been used in recent years. For example, Japanese Laid Open Patent Publication No. 51-9716 discloses a synthetic latex reagent. This synthetic latex is made using a surfactant (an emulsifying agent). Other synthetic latex reagents using surfactants are also known. The usual method of their preparation is to mix together in water an anionic emulsifying agent, a non-ionic one, and a cationic one, and havig added both styrene monomer and an initiator that is soluble in water, to leave the mixture at an appropriate temperature for an appropriate period of time, preferably in an atmosphere without oxygen. In latex synthesized in this way, in general, part of the emulsifying agents used during polymerization are adsorbed onto the surface of the particles of the polystyrene latex, and part are chemically bonded there, with the remainder in the latex in the free state. An equilibrium between adhesion to and release from the surface of the particles of polystyrene latex is reached among these three states. For the production of polystyrene latex by the usual methods such as these, emulsifying agents are indispensible for the formation of stable latex. However, non-adsorbed, free emulsifying agents have an undesirable effect on the aforementioned agglutination reaction of antibody and antigen. In the manufacture of diagnostic reagents, first of all, polystyrene latex such as that described above is sensitized with antigens and antibodies. However, when latex containing emulsifying agents is used, agglutination occurs at this stage. Next, in using latex sensitized with antigen or antibody, the agglutination reaction of the latex will detect the corresponding antibody or antigen that will react with it; if serum containing the antibody or antigen to be detected is brought into contact with the sensitized latex, agglutination occurs. When serum that does not contain such antibody or antigen is brought into contact with the sensitized latex, agglutination will not occur. Nevertheless, with sensitized latex that contains free emulsifying agents, even if negative serum (without antibody or antigen) is brought into contact with it, agglutination will occur, and thus there is often a so-called non-specific agglutination reaction. It is possible to remove emulsifying agents from the latex with ion-exchange techniques or with dialysis, but if this were done, since as mentioned before there is an equilibrium between the emulsifying agents in the free state and those adsorbed onto the surface of the particles of latex, the equilibrium is disturbed, the stability of the latex is greatly damaged, and in practice the latex becomes unusable. Japanese Laid Open Patent Publication No. 57-14610 discloses a method to obtain latex using styrene without emulsifying agents being present, in which styrene is, along with persulfate, the starting materials for polymerization; after polymerization takes place in water, the mixture is made alkaline and heated, giving latex. Latex prepared in this way, when made into a reagent, will not cause non-specific agglutination reactions, because emulsifying agents are not used. Moreover, the stability of the latex is excellent. However, because this latex has a small specific gravity, when it is used as a reagent, when investigating the agglutination characteristics of a specimen, a long period of time is required. In order to obtain latex of high specific gravity, such substances as vinyltoluene, chlorostyrene, methyl methacrylate, vinylchloride, and vinylidene-chloride are polymerized or copolymerized. However, if, for example, chlorostyrene is chosen, since it is highly reactive, it is difficult to control the polymerization reaction. Because monomers remain in the resulting latex, there is an unpleasant odor.